Cat scratch disease (CSD) has been the subject of considerable clinical and microbiological interest for many years. An estimated 24,000 cases of CSD occur each year in the United States, and CSD is responsible for up to 2,000 human hospitalizations. CSD is described as a subacute regional lymphadenitis temporally associated with the scratch or bite of a cat, which occasionally results in meningoencephalitis. Very serious sequelae of CSD have been reported in immunocompromised individuals. The inventors, however, are not aware of any reports of clinical disease in cats despite the fact that cats are the reservoir for the etiologic agent of CSD.
The etiologic agent of CSD is the bacterium Bartonella henselae (B. henselae), formerly called Rochalimaea henselae. See for example, Regnery, et al., 1992, "Serological response to `Rochalimaea henselae` antigen in suspected cat-scratch disease," The Lancet, Vol. 339, pp. 1443-1446; Regnery, et al., 1992, "Naturally occurring `Rochalimaea henselae` infection in domestic cat," The Lancet, Vol. 340, pp. 557-558; U.S. Pat. No. 5,399,485, by Anderson et al, issued Mar. 21, 1995 (Anderson et al, '485); and U.S. Pat. No. 5,644,047, by Anderson et al, issued Jul. 1, 1997 (Anderson et al, '047). Anderson et al, '485, ibid. and Anderson et al, '047, ibid. are each incorporated herein by reference in its entirety. Treatment with antibiotics does not appear to affect the outcome of cat scratch disease. Because cats are the reservoir for B. henselae, they are the source of infection in humans. As such, exposure of humans to B. henselae infection may best be controlled by controlling the bacterium in cats, especially pet cats that have frequent contact with humans.
Many compounds with adjuvant properties are used to enhance the immune response to antigens, but it is unpredictable as to which compound(s) will serve as a suitable adjuvant for a particular antigen. Thus, it is not clear what adjuvants would be suitable to enhance an effective immune response against B. henselae infection. Furthermore, although cats that are experimentally infected with B. henselae are resistant to subsequent infection, it is not known what type of immune response is responsible for this resistance. Thus, as far as the inventors are aware, there is no scientific information to help select an adjuvant that would work.